U.S. patent application number 12/406401 was filed with the patent office on 2009-10-01 for cooking apparatus with thermally shielded temperature sensor.
Invention is credited to Bektas C. Gulkanat, Christian M. Yungbluth.
Application Number | 20090242546 12/406401 |
Document ID | / |
Family ID | 41115552 |
Filed Date | 2009-10-01 |
United States Patent
Application |
20090242546 |
Kind Code |
A1 |
Yungbluth; Christian M. ; et
al. |
October 1, 2009 |
COOKING APPARATUS WITH THERMALLY SHIELDED TEMPERATURE SENSOR
Abstract
A cooking apparatus includes a heating element and a cooking
plate arranged and configured to be heated by the heating element,
the cooking plate having a first surface facing the heating element
and a cooking surface opposite the first surface. A thermostat is
located proximate the first surface and associated with a heating
element control. An insulating heat shield arrangement partially
surrounds the thermostat and shields a shielded portion of the
first surface adjacent the thermostat from direct heating by the
heating element. The insulating heat shield arrangement is
configured to provide a thermal resistance R.sub.h through the
cooking plate between the shielded portion of the first surface at
the thermostat and a directly heated portion of the first surface
outside the shielded portion. The cooking plate is configured such
that a thermal resistance R.sub.c through the cooking plate is
provided between the shielded portion of the first surface at the
thermostat and the cooking surface. The insulating heat shield
arrangement is configured such that thermal resistance R.sub.h is
no less than thermal resistance R.sub.c.
Inventors: |
Yungbluth; Christian M.;
(Charlotte, NC) ; Gulkanat; Bektas C.; (Charlotte,
NC) |
Correspondence
Address: |
THOMPSON HINE LLP;Intellectual Property Group
P.O Box 8801
DAYTON
OH
45401-8801
US
|
Family ID: |
41115552 |
Appl. No.: |
12/406401 |
Filed: |
March 18, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61039631 |
Mar 26, 2008 |
|
|
|
Current U.S.
Class: |
219/448.11 ;
700/97 |
Current CPC
Class: |
H05B 3/68 20130101 |
Class at
Publication: |
219/448.11 ;
700/97 |
International
Class: |
H05B 3/68 20060101
H05B003/68; G06F 19/00 20060101 G06F019/00 |
Claims
1. A cooking apparatus, comprising: a housing; a heating element
located in the housing; a cooking plate arranged and configured to
be heated by the heating element, the cooking plate having a first
surface facing the heating element and a cooking surface opposite
the first surface; a thermostat proximate the first surface and
associated with a heating element control; an insulating heat
shield arrangement partially surrounding the thermostat and
shielding a shielded portion of the first surface adjacent the
thermostat from direct heating by the heating element, the
insulating heat shield arrangement configured to provide a thermal
resistance R.sub.h through the cooking plate between the shielded
portion of the first surface at the thermostat and a directly
heated portion of the first surface outside the shielded portion;
the cooking plate configured such that a thermal resistance R.sub.c
through the cooking plate is provided between the shielded portion
of the first surface at the thermostat and the cooking surface;
wherein the insulating heat shield arrangement is configured such
that the thermal resistance R.sub.h is no less than the thermal
resistance R.sub.c.
2. The cooking apparatus of claim 1 wherein the cooking surface of
the cooking plate is either an upwardly facing surface or a
downwardly facing surface.
3. The cooking apparatus of claim 1 wherein the insulating heat
shield arrangement includes a first heat shield and an adjacent
insulating material.
4. The cooking apparatus of claim 3 wherein the first heat shield
is located proximate the thermostat and the insulating material is
located to an external side of the first heat shield.
5. The cooking apparatus of claim 4 wherein the insulating heat
shield arrangement includes a second heat shield disposed at an
external side of the insulating material.
6. The cooking apparatus of claim 1 wherein the insulating heat
shield arrangement is configured such that the thermal resistance
R.sub.h is at least 105% of the thermal resistance R.sub.c.
7. The cooking apparatus of claim 2 wherein the insulating heat
shield arrangement is configured such that the thermal resistance
R.sub.h is at least 110% of the thermal resistance R.sub.c.
8. The cooking apparatus of claim 1 wherein the first surface is
substantially planar and the thermostat is positioned in contact
with the first surface.
9. The cooking apparatus of claim 1 wherein the first surface
includes a recessed portion, the thermostat is positioned in
contact with the cooking plate in the recessed portion.
10. The cooking apparatus of claim 1 wherein the cooking plate is
formed of a substantially uniform material.
11. The cooking apparatus of claim 1 wherein the cooking plate is
of a laminated configuration using at least two different
materials.
12. A cooking apparatus, comprising: a heating element; a cooking
plate arranged and configured to be heated by the heating element,
the cooking plate having a first surface facing the heating element
and a cooking surface opposite the first surface; a temperature
sensor proximate the first surface and associated with a heating
element control; an insulating heat shield arrangement partially
surrounding the temperature sensor and shielding a shielded portion
of the first surface adjacent the thermostat from direct heating by
the heating element, the insulating heat shield arrangement
configured to provide a through the plate thermal resistance
R.sub.h between the shielded portion of the first surface at the
temperature sensor and a directly heated portion of the first
surface outside the shielded portion; the cooking plate configured
such that a through the plate thermal resistance R.sub.c is
provided between the shielded portion of the first surface at the
temperature sensor and the cooking surface; wherein the insulating
heat shield arrangement is configured such that the through the
plate thermal resistance R.sub.h is at least about 90% of the
through the plate thermal resistance R.sub.c.
13. The cooking apparatus of claim 12 where the through the plate
thermal resistance R.sub.h is leas than about 135% of the through
the plate thermal resistance R.sub.c.
14. The cooking apparatus of claim 13 wherein the through the plate
thermal resistance R.sub.h is between about 95% and 125% of the
through the plate thermal resistance R.sub.c.
15. The cooking apparatus of claim 12 wherein the cooking plate is
formed of a substantially uniform material having substantially the
same thermal resistance per unit length through the material
regardless of direction, and a lateral distance between the
shielded portion of the first surface at the temperature sensor and
the directly heated portion of the first surface outside the
shielded portion is no less than a vertical distance between the
first surface and the cooking surface.
16. A method of designing a cooking plate configuration for a
cooking apparatus, the method comprising the steps of: determining
a location for a thermostat element along a heated surface of the
cooking plate; determining a through the plate thermal resistance
R.sub.c between a cooking surface of the cooking plate and the
defined location of the thermostat element; determining a lateral
distance from the thermostat element that results in a lateral
through the plate thermal resistance R.sub.h that is at least about
90% of the through the plate thermal resistance R.sub.c; and
defining a heat shield configuration that corresponds to the
determined lateral distance.
17. The method of claim 16 wherein the lateral distance determining
step is performed such that the resulting through the plate thermal
resistance R.sub.h is at least as great as the through the plate
thermal resistance R.sub.c.
18. The method of claim 16 wherein the lateral distance determining
step is performed such that the resulting through the plate thermal
resistance R.sub.h is no more than 135% of the through the plate
thermal resistance R.sub.c.
Description
TECHNICAL FIELD
[0001] This application relates generally to a cooking apparatus
and more particularly to a cooking apparatus with improved thermal
shielding for bottom mounted thermostatic devices.
BACKGROUND
[0002] Cooking devices, such as griddle apparatus, are frequently
used in commercial settings for cooking various types of food, such
as hamburgers. The griddle apparatus typically includes a
thermostat control where an operator can set a cooking temperature.
The thermostat control may include a bottom mounted thermostat
probe, bulb or other device that is located beneath the cooking
surface, next to a surface being heated by burners. The thermostat
control should optimally indicate the temperature at the cooking
surface in order to avoid causing the heating element to deactivate
before the cooking surface reaches the set temperature.
SUMMARY
[0003] In an aspect, a cooking apparatus includes a housing, a
heating element located in the housing and a cooking plate arranged
and configured to be heated by the heating element, the cooking
plate having a first surface facing the heating element and a
cooking surface opposite the first surface. A thermostat is located
proximate the first surface and associated with a heating element
control. An insulating heat shield arrangement partially surrounds
the thermostat and shields a shielded portion of the first surface
adjacent the thermostat from direct heating by the heating element.
The insulating heat shield arrangement is configured to provide a
thermal resistance R.sub.h through the cooking plate between the
shielded portion of the first surface at the thermostat and a
directly heated portion of the first surface outside the shielded
portion. The cooking plate is configured such that a thermal
resistance R.sub.c through the cooking plate is provided between
the shielded portion of the first surface at the thermostat and the
cooking surface. The insulating heat shield arrangement is
configured such that thermal resistance R.sub.h is no less than
thermal resistance R.sub.c.
[0004] In another embodiment, where the thermal resistance per unit
length through the plate material is constant regardless of
direction, a lateral distance between the bulb location and a
lateral edge of the heat shield is selected to be no less than that
of a vertical distance between the lower surface and cooking
surface of the plate. In one implementation, the lateral distance
is selected slightly greater than (i.e., between 10 and 30% greater
than) the vertical distance.
[0005] In some implementations, suitable function may be achieved
where the thermal resistance R.sub.h is at least 90%, but no more
than 135% of the thermal resistance R.sub.c (e.g., between 90% and
125% or between 95% and 120%).
[0006] In another aspect, a method of designing a cooking plate
configuration for a cooking apparatus involves: determining a
location for a thermostat element along a heated surface of the
cooking plate; determining a through the plate thermal resistance
R.sub.c between a cooking surface of the cooking plate and the
defined location of the thermostat element; determining a lateral
distance from the thermostat element that results in a lateral
through the plate thermal resistance R.sub.h that is at least about
90% of the through the plate thermal resistance R.sub.c; and
defining a heat shield configuration that corresponds to the
determined lateral distance.
[0007] The details of one or more embodiments are set forth in the
accompanying drawings and the description below. Other features,
objects, and advantages will be apparent from the description and
drawings, and from the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a diagrammatic, section view of an embodiment of a
thermostat control for a griddle apparatus;
[0009] FIG. 2 is another diagrammatic, section view of an
embodiment of a prior art thermostat control for a griddle
apparatus;
[0010] FIG. 3 is a diagrammatic, section view of an embodiment of a
thermostat control for a griddle apparatus according to the present
application;
[0011] FIG. 4 is a heating control plot comparing the
configurations of FIG. 2 and FIG. 3;
[0012] FIG. 5 is another diagrammatic, section view of an
embodiment of a thermostat control for a griddle apparatus
according to the present application;
[0013] FIG. 6 is another diagrammatic, section view of an
embodiment of a thermostat control for a griddle apparatus
according to the present application;
[0014] FIG. 7 is another diagrammatic, section view of an
embodiment of a thermostat control for a griddle apparatus
according to the present application;
[0015] FIG. 8 is another diagrammatic, section view of an
embodiment of a thermostat control for a griddle apparatus
according to the present application;
[0016] FIGS. 9A and 9B depict an exemplary griddle apparatus.
DETAILED DESCRIPTION
[0017] A unique shielding arrangement is provided for bottom
mounted thermostat controls in a griddle application, or other
cooking device application, that provides improved temperature
control.
[0018] Referring to FIG. 1, an exemplary bottom mounted
construction of a hydraulic bulb thermostat control (generally
referred to as element 10) is shown for a griddle apparatus. The
griddle apparatus includes a griddle plate 12 having an upper
cooking surface 14 and a lower surface 16 that is opposite the
cooking surface. While the griddle plate 12 may be a variety of
thicknesses, in some embodiments, the thickness of the griddle
plate may be between about 0.5 and one inch and formed of any
suitable material such as carbon steel. Where the griddle plate is
of a type that is grooved, the overall plate thickness dimension
may be determined as the average plate thickness. The lower surface
16 faces a heating element (represented by elements 15) that is
used to heat the griddle plate 12 to a desired temperature. The
heating element may be a gas burner or an electrical element.
[0019] The thermostat control 10 includes a thermostat bulb 18 in
contact with the lower surface 16 at a contact location C.sub.1 and
inner and outer shields 20 and 22, respectively, partially
surrounding the thermostat bulb. The outer shield 22 shields a
shielded portion 24 of the lower surface 16 defined between
boundaries B.sub.1 and B.sub.2 from radiation, convection and/or
conduction heating by the heating element. An insulated space 25 is
located between the inner and outer shields 20 and 24. Any suitable
insulation 27 may be located in the insulated space, such as rigid
pumous materials, fabric-type insulation or others. While any
suitable geometry may be used for the shields 20 and 22, V-shaped
shields are shown.
[0020] The bottom mounted thermostat provides an indication of (or
approximates) temperature at the cooking surface 14 despite its
position at the bottom of the griddle plate 12. The thermostat bulb
18 senses temperature at its contact point C.sub.1 with the lower
surface 16, and is affected by lateral thermal resistance from a
directly heated surface portion 26 to the thermostat bulb and
vertical thermal resistance from the heat source to the cooking
surface (which is equal to the thickness of the of the griddle
plate assuming a griddle plate of substantially constant thickness
and uniform material).
[0021] In order to provide an indication of temperature at the
cooking surface 14 despite its position at the bottom of the
griddle plate 12, an important parameter for the bottom mounted
thermostat is the relative thermal resistance between it and the
cooking surface 14--that for which the thermostat temperature is
set--and the directly heated surface 26--that surface outside the
shielded portion 24 which is heated directly by the heating
element. In the illustrated embodiment, the shortest distance
D.sub.1 between the thermostat bulb 18 and the heated surface 26 is
along a horizontal line from the contact location C.sub.1 to the
boundary B.sub.1 (B.sub.1 and B.sub.2 may be equidistant from
C.sub.1). The shortest distance D.sub.2 between the thermostat bulb
18 and the cooking surface 14 is typically a straight vertical line
from the contact location C.sub.1 to the cooking surface. With the
griddle plate medium having a constant thermal resistance/per unit
length (regardless of direction), distances D.sub.1 and D.sub.2 are
proportional to the thermal resistances. Where the griddle plate
does not have constant thermal resistance/per unit length (e.g. in
the case of a griddle plate formed by sandwiching two or more plate
materials together), the distances D1 and D2 may not be
proportional to the thermal resistance, in which case a more
considered analysis of the thermal resistance may need to be taken,
particularly in the vertical direction.
[0022] FIG. 2 shows a "small shield" configuration (without the
insulation material shown) of the type used in prior art griddles.
Assuming a uniform plate material in this example, the "small
shield" results in a difference in lateral thermal resistance
(R.sub.h) between the thermostat bulb 18 and heated surface portion
26 as compared to the vertical thermal resistance (R.sub.c) between
the thermostat bulb and the cooking surface 14, whereby R.sub.h is
less than R.sub.c. In this instance, the thermostat bulb 18 will
typically sense and react to the temperature of the heated surface
portion 26 before the cooking surface 14 achieves the set
temperature. While the system will eventually reach steady state
around the set temperature, optimal system performance can be
impacted when R.sub.h<R.sub.c.
[0023] Referring to FIG. 3, an exemplary "large shield"
configuration of the invention is shown (assumed uniform plate
material), which moves the directly heated surface portion 26 a
greater distance D.sub.1 from the thermostat bulb 18 such that it
at least equals the distance D.sub.2 from the cooking surface 14 to
the thermostat bulb (or from the heated surface to the cooking
surface) such that the thermal resistance R.sub.h at least equals
or is greater than the thermal resistance R.sub.c. In this
embodiment, a span S (D.sub.1 times two) of the outer shield 22 is
selected to increase the distance D.sub.1. For R.sub.h>R.sub.c,
no significant difference between performance curves is expected.
Since exact border positions between the heated surface 26 and
shielded portion 24 can be difficult to pinpoint precisely, in some
cases it may be desirable, though not required, to select a nominal
distance of approximately 1/8 inch (or other suitable dimension)
greater than the distance D.sub.2 to ensure that the desired
boundaries are exceed, but not excessively so, and to account for
possible perturbations in the manufacturing process. For the large
shield configuration of FIG. 3, the distance D.sub.1 to the heated
surface 26 from the contact point C.sub.1 is greater than the
distance D.sub.2 from the cooking surface 14, thus a temperature
change at the cooking surface due to application of heat to surface
26 will occur more rapidly than a temperature change at the bulb
location C1. While not shown, insulation material would be located
between the shield 22 and the shield 20 (e.g., per FIG. 1).
[0024] FIG. 4 shows data illustrating the effect of the smaller
versus larger shield configurations. The data of FIG. 4 reflects a
comparative test using identical thermostats on the same griddle
plate, each set to 350.degree. F., but in one case shielded using a
prior art "small shield" approach and in the other case using the
inventive "large shield" approach. The thickness of the griddle
plate, which is of a uniform material, is 0.875 inch thick, and the
R.sub.h distances for the small and large shields are 0.71 inch and
1.07 inch, respectively. The griddle plate being heated using a
natural gas burner.
[0025] As can be seen by FIG. 4, when R.sub.h is smaller than
R.sub.c, system response is driven by R.sub.h and the heating
element is turned off before the cooking surface achieves the set
temperature. When R.sub.h is greater than R.sub.c, the cooking
surface will achieve set temperature more rapidly and cycle
normally. When the cooking surface is loaded (e.g., cooled via
contact with cold food product), this response curve will be
repeated continuously. Since accurate temperature response to
product loading (recovery) is important to this class of cooking
device, the above-described large shield approach can significantly
improve recovery performance.
[0026] It is recognized that alternative probe mount configurations
are possible, such as providing a slight upward recess along the
bottom surface, and placing the thermostat shield in the recess
(e.g., per FIG. 5), in which case the thermal resistance
measurement R.sub.h may actually be taken at a slight angle
relative to the main plane of the lower surface and/or may involve
evaluation of a non-linear resistance path through the plate, as
shown.
[0027] Although a thermostat bulb having a single point or line of
contact with the griddle plate is primarily shown, it is recognized
that alternative configurations are possible. For example, a
thermostat 18' having a generally flat configuration, such as that
shown in FIG. 6, would have a plane of contact with the lower
surface of the griddle plate. In such an arrangement, the
appropriate location for measurement of the lateral thermal
resistance R.sub.h would be at the edge of the plane of contact as
shown. While not shown, insulation material would be located
between the shield 22 and the shield 20.
[0028] FIG. 7 shows an alternate shielding configuration utilizing
three shields 30, 32 and 34. In this configuration, the
representative locations for measuring R.sub.h and R.sub.c are
shown. Insulation would be located between shields 30 and 32. The
space between shields 32 and 34 could include insulation, or could
simply be an air gap.
[0029] Referring to FIG. 8, alternative arrangement having only a
single shield 30 is provided, with thick insulation material 70
surrounding the shield. In this arrangement, the reference for
measuring thermal resistance R.sub.h is to the edge of the
insulation material itself.
[0030] Referring now to FIGS. 9A and 9B, an exemplary griddle
apparatus 40 is shown along with and exemplary gas feed system 42
(that is located within the unit). Thermostatic valves 44 and 46,
each of which controls gas flow to a respective burner (e.g., 47),
include respective lines 48 and 50 running to respective thermostat
bulbs (e.g., bulb 18 of FIG. 3). The thermostat valves act as
heating element controls based upon the temperature feedback from
the respective thermostat bulbs. The ON/OFF (or OPEN/CLOSE)
temperature setpoint of each valve 44, 46 is adjustable manually
via a user control knob 52, 54.
[0031] It is to be clearly understood that the above description is
intended by way of illustration and example only and is not
intended to be taken by way of limitation, and that changes and
modifications are possible. For example, while a griddle apparatus
is primarily described, the inventive concepts could be utilized in
connection with other cooking plate devices, such as braising pans.
Moreover, although a griddle plate with an upwardly facing cooking
surface is primarily shown and described, the shielding
arrangements could be implemented on a top griddle plate (e.g., the
upper griddle plate of a clamshell type griddle 70 having both an
upper griddle plate 72 and a lower griddle plate 74 per the
schematic of FIG. 9, where the cooking surface of upper plate 72
faces downward when in the cooking position). Accordingly, other
embodiments are contemplated and modifications and changes could be
made without departing from the scope of this application.
* * * * *